Buffing structure for rear end travel of hydraulic cylinder

ABSTRACT

A buffing structure for rear end travel of hydraulic cylinder. The central portion of the bottom of the piston of the hydraulic cylinder is formed with an internal hole which axially extends through the piston and deeply extends into the piston stem. The internal hole has a large vent and a small vent which radially pass through the piston stem. The small vent is adjacent to the joint between the piston stem and an end face of the piston facing the rear end cap. The large vent is formed at a rear end of the internal hole deeply in the piston stem. The large vent is axially spaced from the small vent by a certain distance. When the piston moves to a position near the rear end cap of the hydraulic cylinder, the large vent is first sunk into the rear end cap and blocked. At this time, the oil can only flow through the small vent with smaller cross-sectional area so as to reduce oil flow and achieve a buffing effect.

BACKGROUND OF THE INVENTION

[0001] The present invention is related to a buffing structure for rear end travel of hydraulic cylinder, and more particularly to a buffing structure for rear end travel of all-liquid single-acting hydraulic cylinder.

[0002]FIG. 4 shows a conventional all-liquid, single-acting hydraulic cylinder 8. One end of the piston 81 of the hydraulic cylinder 8 opposite to the piston stem 82 has a projecting post 821. The cap 83 at the front end of the hydraulic cylinder 8 is formed with an accommodating cavity 84 cooperating with the projecting post 82. The accommodating cavity 84 communicates with an oil outlet 85. The cap 83 is further formed with two small diameter flow ways 86, 87 which also communicate with the oil outlet 85. A check ball 88 is disposed in one flow way 87, whereby the oil can only one-way flow therethrough during the pushing travel of the piston 81.

[0003] The piston 81 is formed with an internal hole 822 deeply extending into the piston stem 82. The internal hole 822 has a vent 823 formed on the joint between the piston 82 and the piston 81. The vent 823 radially passes through the piston stem 82.

[0004] Referring to FIG. 5, when the piston 81 moves toward the cap 83 at the front end, the oil in the hydraulic cylinder 8 flows out through the accommodating cavity 84 from the oil outlet 85. When the piston 81 moves to the front end of the hydraulic cylinder 8, the projecting post 82 is fitted into the accommodating cavity 84 to block the way thereof. At this time, the oil in the hydraulic cylinder 8 can only flow through the small diameter flow way 86 into the accommodating cavity 84 and then flow out from the oil outlet 85. The flow way 86 has small cross-sectional area so that little oil flow is drained out from the hydraulic cylinder 8 and the back pressure is increased to buff the moving speed of the piston 81.

[0005] Referring to FIG. 6, when the piston 81 is to move toward the cap 89 at the rear end of the hydraulic cylinder 8, the oil between the piston 81 and the rear cap 89 will flow through the vent 823 and the internal hole 822 into the space between the piston 81 and the front cap 83. Therefore, the piston 81 can move toward the rear cap 89.

[0006] According to the above design of flow ways of the front cap 83, a buffing effect is achieved when the piston 81 moves toward the front cap 83. However, the piston stem 82 must pass through the rear cap 89 so that it is impossible to design the rear cap 89 with the same structure as the front cap 83. Accordingly, when the piston 81 moves the rear end of the hydraulic cylinder 8, the piston 81 will collide the rear cap 89 at the original moving speed to cause noise and damage. Therefore, it is necessary to provide a buffing structure for rear end of all-liquid single-acting hydraulic cylinder.

SUMMARY OF THE INVENTION

[0007] It is therefore a primary object of the present invention to provide a buffing structure for rear end travel of hydraulic cylinder. The piston of the hydraulic cylinder is formed with an internal hole which axially extends through the piston and deeply extends into the piston stem. The internal hole has a large vent and a small vent which radially pass through the piston stem. The small vent is adjacent to the joint between the piston stem and an end face of the piston facing the rear end cap. The large vent is formed at a rear end of the internal hole deeply in the piston stem. When the piston moves to a position near the rear end cap of the hydraulic cylinder, the large vent is first sunk into the rear end cap and blocked. At this time, the oil can only flow through the small vent with smaller cross-sectional area so as to reduce oil flow and achieve a buffing effect for the travel of the piston.

[0008] The present invention can be best understood through the following description and accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a sectional view of the structure of the present invention;

[0010]FIG. 2 is a sectional view showing the movement of the piston of the present invention;

[0011]FIG. 3 is a sectional view showing that the piston is moved to the rear end to achieve a buffing effect;

[0012]FIG. 4 is a sectional view of a conventional all-liquid single-acting hydraulic cylinder;

[0013]FIG. 5 is a sectional view of the conventional all-liquid single-acting hydraulic cylinder, showing the movement of the piston in one state; and

[0014]FIG. 6 is a sectional view of the conventional all-liquid single-acting hydraulic cylinder, showing the movement of the piston in another state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] Please refer to FIG. 1 which shows a part of the hydraulic cylinder 1 of the present invention which has a rear end cap 15. A piston 11 is disposed in the hydraulic cylinder 1 and coupled with a piston stem 12 passing through the rear end cap 15 of the hydraulic cylinder. The central portion of the bottom of the piston 11 is formed with an internal hole 121 which axially extends through the piston 11 and deeply extends into the piston stem 12. The internal hole 121 has a large vent 13 and a small vent 14 which radially pass through the piston stem 12. The small vent 14 is adjacent to the joint between the piston stem 12 and an end face 111 of the piston 11 facing the rear end cap 15. The large vent 13 is formed at a rear end 122 of the internal hole 121 deeply in the piston stem 12. The large vent 13 is axially spaced from the small vent 14 by a certain distance.

[0016] Referring to FIG. 2, when the piston 11 is pushed by the oil toward the rear end cap 15, the oil in the space 10 on left side of the piston 11 flows through the large and small vents 13, 14 and then flows from the internal hole 121 into the space 20 on right side of the piston 11. Accordingly, the piston 11 can move within the hydraulic cylinder 1. When the piston 11 moves to a position near the rear end cap 15 of the hydraulic cylinder 1, the large vent 13 is first sunk into the rear end cap 15 and blocked as shown in FIG. 3. At this time, the oil in the left space 10 can only flow from the small vent 14 with smaller cross-sectional area through the internal hole 121 into the right space 20. Due to the smaller cross-sectional area of the small vent 14, the oil flow is reduced so as to decrease the moving speed of the piston 11 and achieve a buffing effect.

[0017] The above embodiment is only used to illustrate the present invention, not intended to limit the scope thereof. Many modifications of the above embodiment can be made without departing from the spirit of the present invention. 

What is claimed is:
 1. A buffing structure for rear end travel of hydraulic cylinder, a piston being disposed in the hydraulic cylinder and coupled with a piston stem passing through a rear end cap of the hydraulic cylinder, a central portion of the bottom of the piston being formed with an internal hole which axially extends through the piston and deeply extends into the piston stem, the internal hole having a large vent and a small vent which radially pass through the piston stem, the small vent being adjacent to the joint between the piston stem and an end face of the piston facing the rear end cap, the large vent being formed at a rear end of the internal hole deeply in the piston stem, the large vent being axially spaced from the small vent by a certain distance. 